vocals - How do I start with effects

i just bought an Effect processor(Lexicon MX300)to be used in my church.

I want to use it to enhance the worship leader's singing experience. I wish to be introduced with some programs and recommended setting for a start for mixing some effect into the vocal.

Later on, i will also be using it on an acoustic guitar.

Thanking you inadvance
Johnny

Did the Lexicon come with an instruction manual? I have used that unit before. It is a nice piece of equipment but I did have a hard time navigating through it. the Lexicon MX300 is mainly a reverb unit. It can make your vocalist sound like it is singing in many different places. ( a Hall, Stadium, Bathroom, Club, Etc) Reverb is one of the best tools for making the vocals sound "larger then life". There should be many presets that come with the unit. You should plug in a microphone and do some tests and find some patches you like. Then get someone to sing through it and find the best patch for the room your in. I don't know the room that you will be singing in but make sure the effect is not to over bearing. You can mainly control that with 2 features that are in this unit.

1. Wet/Dry Mix - The could also be called the effect level. The reverb of the room your in plus the reverb in this unit could drown out the singer, make sure there is an even balance. 
2. Pre Delay - Lets say that you were testing the unit and the pre delay was set to 1 second. If you said the word "test" in the microphone. You would automatically hear yourself say the word through the speakers, but then 1 second later you would hear the word "test" again with a reverb effect. Play around with the pre delay until it sounds good in the room.

There is one way to test if your settings are right. Get someone to sing through the microphone while you stand at the back of the room. If the vocals still sound good there your doing something right. Remember that a empty room sounds different then a room full of people.  If you did your tests in a empty room, you might want to turn up the final effect to even things out.

Best of luck, let me know how things turn out